Unless you are integrating some of your existing nape hair you will have to go lower. My full caps extend all the way down to where I want my back hairline to start.

With a little trial and error I was able to develop a neckline base modification and attachment method that gives a strong, undetectable hold using blue liner tape. In the past people complained about how the flexing in the neck area would not allow the unit to stick for any length of time, but there are several guys out there now who are wearing full caps that do not have issues in the back.

If you are not integrating nape hair you can always make the base extend down a little further than you think you might want and trim the base up after your cut-in with a hobby knife if you think it might look better or stay attached better if the back were a little higher.

And to answer your question- no, the back will not have a problem flapping in the wind as long as you use blue liner or a strong glue, especially with a fairly fresh attachment.

Here is a picture of the back of my last full cap. The hair extends approximately 1/2" below the base. This should give you an idea of where the lace begins.